From the past, an O-ring, a paste material, oil with high viscosity, or the like has been used as a mechanism to seal a gap between an atmospheric pressure side and a vacuum side, for example. Particularly, in a seal method for a rotation introducing mechanism to introduce a rotation drive force from an atmospheric pressure side to a vacuum side, a lubricating material such as a grease (with low viscosity) or lubricating oil that also functions to reduce friction at a friction/sliding portion may be used as a seal material. As the lubricating material as described above, a magnetorheological fluid may be used (see, for example, Patent Document 1, paragraph [0032] of the specification).
Since the lubricating material as described above is expendable, maintenance such as replenishment of a lubricating material is required, for example. Particularly, in the rotation introducing mechanism described above, a lubricating material is leaked to the vacuum side little by little, so the replenishment of the lubricating material is required.
Patent Document 1: Japanese Patent Application Laid-open No. 2007-258573